1. Field of the Invention
The present invention relates to vehicle co-operative control systems comprising a combination of a driving force and/or braking force distribution device which distributes the driving force or braking force between the right and left wheels or between the front and rear wheels and an electric power steering device which applies a steering assist torque to the steering system.
2. Description of the Prior Art
There is a known technique for enhancing the turning performance of a vehicle where the ratio by which the engine driving force is distributed between the right and left driven wheels is made variable, and the driving force distributed to the outer turning wheel is increased while the driving force distributed to the inner turning wheel is decreased so as to generate a yaw moment in the turning direction. In a vehicle having such a driving force distribution device, there is the problem that when the driving forces distributed to the right and left driven wheels are varied, an undesirable steering force is produced in the right and left driven wheels which also serve as steering wheels (the torque steer phenomenon). Therefore, the present assignee has already made a proposal in which the torque steer phenomenon is suppressed by utilizing an electric power steering device which is provided in the vehicle and generating a steering assist torque in the electric power steering device so as to counteract the above-mentioned undesirable steering force (ref. Japanese Patent Application Laid-open No. 11-129927).
In the above-mentioned prior art system, a circuit for generating a steering assist torque which suppresses the torque steer phenomenon is incorporated beforehand into the control means for controlling the electric power steering device. On the other hand, in the case of vehicles having a specification in which a driving force distribution device is not provided, it is unnecessary to incorporate a circuit for generating a steering assist torque which suppresses the torque steer phenomenon, into the control means for controlling the electric power steering device, and therefore it is necessary to change the design of the above-mentioned control means according to whether or not the specification of the vehicle includes a driving force distribution device, thus resulting in a high cost.
The present invention has been carried out in view of the above-mentioned circumstances, and it is an objective of the present invention to provide a vehicle co-operative control system for suppressing the torque steer phenomenon by co-operatively controlling a driving force and/or braking force distribution device and an electric power steering device, wherein without changing the control means of the electric power steering device of a vehicle having a specification in which the co-operative control is not carried out or with the addition of only a minimal change, the control means can be applied to a vehicle having a specification in which the co-operative control is carried out.
In order to achieve the above-mentioned objective, this first characteristic of the present invention is a vehicle co-operative control device comprising a driving force and/or braking force distribution device for distributing the driving force or braking force between the right and left wheels or between the front and rear wheels, a first control means for controlling the operation of the driving force and/or braking force distribution device, an electric power steering device for applying a steering assist torque to a steering system, and a second control means for controlling the operation of the electric power steering device based on at least the steering torque detected by a steering torque detecting means. The steering torque detected by the steering torque detecting means is input into the first control means and the first control means calculates a corrected steering torque by correcting the steering torque according to the degree of control of the driving force and/or braking force distribution device and outputs it to the second control means. The second control means calculates the steering assist torque based on the corrected steering torque.
In accordance with the above arrangement, the steering torque detected by the steering torque detecting means is not directly input into the second control means of the electric power steering device; instead the steering torque is input into the first control means of the driving force and/or braking force distribution device and is corrected according to the degree of control of the driving force and/or braking force distribution device. The corrected steering torque is input into the second control means so as to calculate the steering assist torque of the electric power steering device and, therefore, the second control means of a vehicle in which co-operative control between the electric power steering device and the driving force and/or braking force distribution device is not carried out, can be used without modification so as to effect the co-operative control thus contributing to a reduction in cost.
A second characteristic of the present invention is a vehicle co-operative control device comprising a driving force and/or braking force distribution device for distributing the driving force or braking force between the right and left wheels or between the front and rear wheels, a first control means for controlling the operation of the driving force and/or braking force distribution device, an electric power steering device for applying a steering assist torque to a steering system, and a second control means for controlling the operation of the electric power steering device based on at least the steering torque detected by a steering torque detecting means. The first control means calculates an amount of steering torque correction according to the degree of control of the driving force and/or braking force distribution device and outputs it to the second control means, and the second control means calculates the steering assist torque based on a value obtained by adding or subtracting the amount of steering torque correction to or from the steering torque detected by the steering torque detecting means.
In accordance with the above arrangement, the first control means of the driving force and/or braking force distribution device calculates an amount of steering torque correction according to the degree of control of the driving force and/or braking force distribution device. The second control means into which the amount of steering torque correction has been input, calculates a steering assist torque for the electric power steering device based on the value obtained by adding or subtracting the amount of steering torque correction to or from the steering torque detected by the steering torque detecting means. Therefore the co-operative control can be carried out while minimizing changes made to the second control means of a vehicle which does not carry out co-operative control between the electric power steering device and the driving force and/or braking force distribution device, thus contributing to a reduction in cost.
A third characteristic of the present invention is a vehicle co-operative control device comprising a driving force and/or braking force distribution device for distributing the driving force or braking force between the right and left wheels or between the front and rear wheels, a first control means for controlling the operation of the driving force and/or braking force distribution device, an electric power steering device having a motor for applying steering assist torque to the steering system, and a second control means for calculating a steering assist control signal for driving the motor based on at least the steering torque detected by a steering torque detecting means. The first control means can calculate a torque steer prevention control signal for driving the motor based on the degree of control of the driving force and/or braking force distribution device, and the second control means comprises a switch over means which provides an output to the electric power steering device by selecting either one of the steering assist control signal and the torque steer prevention control signal according to the operational status of the driving force and/or braking force distribution device.
In accordance with the above arrangement, when the driving force and/or braking force distribution device has a non-operational status, control of the motor of the electric power steering device is based on the steering assist control signal calculated by the second control means. When the driving force and/or braking force distribution device has an operational status, the switch over means provided on the second control means is switched over so that the drive of the motor of the electric power steering device is based on the torque steer prevention control signal calculated by the first control means. Therefore by carrying out only the minimal change of adding a switch over means to the second control means of a vehicle which does not carry out co-operative control between the electric power steering device and the driving force and/or braking force distribution device the co-operative control can be effected, thus contributing to a reduction in cost.
In addition to the third characteristic, a fourth characteristic of the present invention proposes a vehicle co-operative control device in which the switch over means gradually carries out the switch over between a steering assist control signal and a torque steer prevention control signal.
In accordance with the above arrangement, since the switch over between the steering assist control signal and the torque steer prevention control signal is carried out gradually, rapid changes to the steering assist torque added to the steering system which cause the driver to experience an unpleasant sensation can be prevented.
A fifth characteristic of the present invention is a vehicle co-operative control device comprising a driving force and/or braking force distribution device for distributing the driving force or braking force between the right and left wheels or between the front and rear wheels, a first control means for controlling the operation of the driving force and/or braking force distribution device, an electric power steering device having a motor for applying steering assist torque to a steering system, and a second control means for calculating a motor control signal for driving the motor based on at least the steering torque detected by a steering torque detecting means. The first control means can calculate a correction signal for correcting the motor control signal based on the degree of control of the driving force and/or braking force distribution device, and the second control means comprises an addition and subtraction means which adds or subtracts the correction signal to or from the motor control signal.
In accordance with the above arrangement, the first control means for controlling the driving force and/or braking force distribution device calculates a correction signal according to the degree of control of the driving force and/or braking force distribution device, and the second control means for controlling the electric power steering device, drives the motor by adding or subtracting the amount of the correction signal to or from the motor control signal. Therefore the co-operative control is enabled by carrying out only the minimal change of introducing an addition and subtraction means to the second control means of a vehicle which does not carry out co-operative control between the electric power steering device and the driving force and/or braking force distribution device, thus contributing to a reduction in cost.